This invention relates to blends of fluoropolymer and plasticized poly(vinyl chloride) and its copolymers.
Fluoropolymers and PVC compounds are widely used in various wire and cable applications. For example, category 3 plenum cables typically consist of PVC plenum compounds as the insulation and jacket materials. Category 5 cables typically consist of fluoropolymers as insulation material and PVC plenum compounds as the jacket material. The fluoropolymer commonly used is FEP (fluorinated ethylene/propylene copolymer). Category 6 and 7 cables consist of fluoropolymers as insulation and jacket materials. FEP is typically the fluoropolymer used in these applications.
Fluoropolymers have been used as processing aids in polymer blend compositions for some time. For example, U.S. Pat. No. 4,904,735 (Chapman, Jr., et al.), U.S. Pat. No. 5,013,792 (Chapman, Jr., et al.), and U.S. Pat. No. 5,132,368 (Chapman, Jr., et al.) disclose using a minor amount of one or more fluoropolymers as a processing aid in a difficultly melt-processible polymer. The amount of fluoropolymer used as a processing aid is typically less than a couple of percent.
The process of grafting fluoropolymers is known in the prior art. For example, U.S. Pat. No. 5,576,106 (Kerbow et al.) discloses a process for grafting an ethylenically unsaturated compound onto the surface of the particles of fluoropolymer powder. The ethylenically unsaturated compound provides polar functionality to the fluoropolymer. The utility of the resultant grafted fluoropolymer powder is disclosed to act as an adhesive to adhere dissimilar materials together, such as tetrafluoroethylene/ethylene (ETFE) copolymer to polyamide.
The use of a methylacrylic polymer as a compatibilizer is also known in the prior art. For example, U.S. Pat. No. 6,054,538 (Thulliez et al.) discloses compositions based on vinylidene fluoride copolymers plus PVC, and an effective amount of methylacrylic polymer as a compatibilizer. The weight ratio of vinylidene fluoride copolymer to PVC is at least 1.2. That means the blend contains more than 50 wt % of fluoropolymer in the blend.
The fluoropolymers mentioned in these disclosures are not suitable to be mixed with PVC. Several inherent barriers inhibit the blending of PVC with fluoropolymers by conventional means. The barriers include differences in compatibility and processing temperatures. A development of PVC/fluoropolymer blends would enhance the properties of PVC blend compounds to be used in high frequency cable applications. There is a need for polymer blends with a blend ratio of PVC to fluoropolymer larger than 1.0 with good mechanical properties and electrical properties for high frequency cable applications.
It is therefore an object of this invention to provide a blend of PVC/fluoropolymer for wire and cable applications.
The object set forth above as well as further and other objects and advantages of the present invention are achieved by the embodiments of the invention described hereinbelow.
It has now been discovered that acrylate-grafted fluoropolymer can be melt-blended with plasticized PVC and fluoropolymer to produce a dispersion of the fluoropolymer in a matrix of plasticized PVC, so as to provide improvements of tensile elongation, dielectric properties, flame retardancy, and reduction of smoke generation for use in wire and cable applications. In one aspect, the present invention provides a melt-mixed blend, comprising plasticized PVC as the matrix of the blend and fluoropolymer as the dispersed phase and the acrylate-grafted fluoropolymer as the compatibilizer to improve the dispersion of fluoropolymer. The melt-mixed blend has improved electrical and physical properties for use in high frequency wire and cable applications.
The melt-mixed blend of the present invention comprises a plasticized PVC, a fluoropolymer and an acrylate-grafted fluoropolymer.
PVC resins that can be used in this invention as the PVC component of the melt-mixed blend are homo PVC or copolymer of PVC, with an IV ranging from 0.8 to 1.4.
The PVC is present as the matrix of the melt-mixed blend of the present invention. That is, the PVC component forms the continuous phase of the melt-mixed blend.
With respect to the fluoropolymer component of the melt-mixed blend of the present invention, a wide variety of fluoropolymers can be used which are melt-extrudable at a temperature less than 230xc2x0 C.
The fluoropolymers are the copolymers of ethylene with perhalogenated monomers such as tetrafluoroethylene (TFE) or chlorotrifluoroethylene (CTFE), such copolymers being often referred to as ETFE and ECTFE, respectively. In the case of ETFE, minor amounts of additional monomer are commonly used to improve properties such as reduced high temperature brittleness. Perfluoro(propyl vinyl ether) (PPVE), perfluoro(ethyl vinyl ether) (PEVE), perfluorobutyl ethylene (PFBE), and hexafluoroisobutylene (HFIB) are preferred additional comonomers. ECTFE may also have additional modifying comonomer.
The preferred fluoropolymers are ECTFE. U.S. Pat. No. 5,962,610 (Abusleme, et al) describes ethylene fluoro-containing copolymers of the ECTFE and ETFE type. Such fluoropolymers are usually partially-crystalline as indicated by a non-zero heat of fusion associated with a melting endotherm as measured by DSC on first melting. In the present invention, two different grades of a commercial ECTFE powder (Halar 353, Ausimont and Halar 476, Ausimont) were used which could be subsequently processed at a temperature below 210xc2x0 C.
Though the exact composition of the two grades of ECTFE was not provided by the supplier, the published literature suggests that both powders contain at least 40 to 60 molar percent of ethylene (C2H4). See xe2x80x9cCopolymerization of Ethylene and Chlorotrifluoroethylene by Trialkylboron Catalysts-II. Physico-Chemical Characterization of the Copolymersxe2x80x9d by C. Garbuglio et al., European Polymer Journal, Vol. 3, pp 137-144 (1967).
Other fluoropolymers that can be used include vinylidene fluoride polymers including homopolymers and copolymers with other perfluoroolefins, particularly hexafluoropropylene (HFP), and chlorotrifluoroethylene (CTFE), and optionally TFE. TFE/HFP copolymer which contains a small amount of vinylidene fluoride, which copolymer is often referred to as THV, can also be used. When vinylidene fluoride polymer is used, the technological application of the blends is not for high frequency cables.
In one aspect of this invention, the fluoropolymer is functionalized by having an acrylate grafted thereto, which imparts compatibility to the blends of PVC and fluoropolymers. More particularly, the grafting is done by melt mixing a fluorine-containing polymer having hydrogen atoms bonded to main-chain carbon atoms, a grafting compound such as methyl methacrylate (MMA), butyl methacrylate (BMA), vinyl acetate, and butyl acrylate, and a radical-forming agent (peroxide). Preferably, the reaction composition is further purified by precipitation into cold acetone from a hot xylene solution. In attempts to evaluate this grafting technology, FTIR is used to confirm the existence of acrylate-grafted copolymer.
The amount of grafted-ECTFE copolymer used in the blend is in an amount that is effective to improve the dispersion of fluoropolymer in melt mixing of the blend of plasticized PVC and fluoropolymer. Generally, the amount of grafted copolymer is in the range of 2.0 wt % to 30 wt % based on the total weight of the resultant PVC and fluoropolymer. Preferably, the amount of grafted ECTFE copolymer is 3 to 10 wt %, more preferably 3 to 6 wt %. The acrylate grafted ECTFE copolymer is prepared prior to the melt blending of PVC and ECTFE.
As one skilled in the art will recognize, it is possible to carry out other chemical reactions of different functionality-grafted fluoropolymer to alter the grafted entity and thereby achieve different effects. Products of derivative reactions can be maleic anhydride, caprolactone, and acrylic acid.
The acrylate-grafted fluoropolymer improves the dispersion of fluoropolymer when melt-mixed with PVC and fluoropolymer. That is, the presence of the acrylate-g-ECTFE copolymer makes the fluoropolymer generally well dispersed (uniformly dispersed) in the blend.
The incorporation of the acrylate-g-ECTFE results in the melt-mixed blend of the invention having surprisingly good mechanical properties, improved dielectric properties, and reduced smoke generation, and improved flame properties that is useful for wire and cable applications.
The melt-mixed blend of the present invention is preferably prepared by melt blending the ingredients together under high shear. The ingredients can first be combined in desired proportions and blended with each other in the dry state, such as by tumbling in a drum, or can be combined by simultaneous or separate metering of the feed of one or more of the components to the melt blending device. Preferably, the melt blending is done in a twin screw extruder, such as manufactured by Werner and Pfleiderer or by Berstorff. Numerous other high shear melt blending devices, such as a counter-rotating twin screw extruder, Banbury internal mixer, as known to those skilled in the art, can be used without departing from the spirit of the invention.
One skilled in the art will recognize that the acrylate-grafted fluoropolymer component used to prepare a melt-mixed blend of the present invention can itself be a blend. Thus, for example, the acrylate-grafted fluoropolymer component can be a blend of two or more acrylate-grafted fluoropolymers. Additionally, the fluoropolymer component in the melt-mixed blend of the present invention may itself be an acrylate-grafted fluoropolymer, or a blend of acrylate-grafted fluoropolymer and a fluoropolymer.